Many currently-manufactured cathode ray tubes, such as those employed in color television and allied video applications, conventionally utilize patterned screens comprised of respective groups of related phosphor materials in conjunction with a windowed webbing evidencing an array of interstices. A color screen structure of this type is conventionally referred to as a matrix or composite screen.
While matrix screens provide enhanced color displays, there is, because of economic considerations, a demand for color cathode ray tubes having non-matrix screens, i.e., those wherein the patterned array of phosphor elements is utilized without the benefits of the interstitial webbing. Such screens were conventional before the advent of the matrix screen concept, and are less costly to produce.
In the manufacture of non-matrix screen CRT's, it is common practice to apply the patterned phosphor screen on the interior surface of the panel viewing area by conventional photo exposure techniques. This is followed by applying a thin film of lacquer over the back of the screen and the interior of the panel. Next, a thin layer of aluminum is vapor disposed thereover to provide a uniform conductive mirror-like covering of the screen and surrounding sidewalls of the panel. The aforementioned intermediate lacquer film, in addition to provide a substantially smooth surface for supporting the reflective aluminum, also prevents the aluminum from penetrating and poisoning the phosphor particles comprising the screen. The aluminized panel is then baked to remove the lacquer which is volatilized through the substantially porous structure of the aluminum. Thus, a conductive reflective coating is disposed on the back of the screen and the surrounding sidewalls of the panel.
In certain CRT applications, the tube is mounted in a manner whereby the panel portion projects slightly through an opening in the front of the display cabinet. This type of "push-through" mounting prominently exposes a peripheral screen-framing band of the sidewall disposed aluminum. Thus, in tubes intended for such utilization, it is aesthetically important that the aluminizing on the sidewall of the panel be free of noticeable and distracting blemishes. But, such quality is not always achieved since volatilization of the lacquer, during panel baking, sometimes results in blistering of the overlying aluminum film disposed on the glass sidewall areas. This undesired situation not only creates a poor cosmetic appearance and reduced conductivity, but also produces a potentially deleterious loose-particle problem within the tube.
In addition, in those tubes using a flexural contactor to accomplish electrical connection between the screen-related mask and the conductively coated sidewall of the panel, the sole thin layer of aluminum disposed thereon often proves to be an inadequate conductive medium. The mask-mounted flexural contactor pressured against the aluminum coating tends to cause abrasion thereof, producing pernicious metallic residue in the mask-screen region of the tube.